1. Field of the Invention
The present invention relates to an ink jet recording method which enables a multi-color image of a high quality to be recorded on an inexpensive recording medium by inks of different colors, with superior recording characteristics such as ink absorption, coloring (optical density), chromaticity, hue, sharpness and image preservation.
2. Description of the Related Arts
Various recording mediums suitable for ink jet recording have been proposed and used. For instance, Japanese Patent Laid-Open Publication No. 56-148585 discloses a recording medium which is composed of a substrate made of a paper having a small ink absorption characteristic, e.g., a wood-free paper, and an ink absorption layer formed on the substrate and made of a porous inorganic pigment. When this recording-medium is used for recording a color image of high quality and resolution, it is necessary that the ink absorption layer have a considerably large thickness in order to quickly absorb a large quantity of ink. This causes inconveniences such as generation of paper dust, inferior writing characteristic, difficulty in the production of the recording medium, and rise in the production cost.
A recording medium also is known in which, as disclosed in Japanese Patent Laid-Open Publication No. 59-185690 for example, a porous pigment layer is formed on a liquid-absorbing substrate paper which is prepared with a low degree of sizing. This type of recording medium is advantageous in that generation of paper dust is suppressed and the production cost is lowered, while a superior ink absorption characteristic is obtained even with a thin ink acceptor surface layer.
The known recording mediums described above, however, suffer from common disadvantages in that hues are changed or chromaticity is seriously impaired in color mixing regions where ink droplets of different colors are deposited one on the other.
In general, an ink jet recording method is capable of producing color images of high quality and resolution and, hence, there are demands for stable preservation of such images. In particular, the problem of indoor discoloration of a recorded image, peculiar to coated papers, is becoming a matter of great concern.
Hitherto, fastness of images exposed to lights has been recognized as an important factor for preventing discoloration of images, which is caused by exposure of the recorded images to ultraviolet rays and visible rays, regardless of the types of recording mediums such as ordinary PPC (plain-paper copier) papers and wood-free papers, as well as coated paper specifically designed for ink jet recording. Indoor discoloration, however, takes place on images formed on coated papers when such papers are kept from sunlight, but never occurs on images which are recorded on non-coated papers such as PPC papers. Thus, indoor discoloration is a problem peculiar to coated papers and, therefore, has to be discussed separately from light-fastness of images.